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Search Results: 1 - 10 of 593 matches for " Maximilian Weigend "
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Total Control – Pollen Presentation and Floral Longevity in Loasaceae (Blazing Star Family) Are Modulated by Light, Temperature and Pollinator Visitation Rates
Tilo Henning, Maximilian Weigend
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0041121
Abstract: Stamen movements can be understood as a mechanism influencing pollen presentation and increasing outbreeding success of hermaphroditic flowers via optimized male function. In this study we experimentally analyzed the factors regulating autonomous and thigmonastic (triggered by flower visitors) stamen movements in eight species of Loasaceae. Both types of stamen movements are positively influenced by light and temperature and come to a virtual standstill in the dark and at low temperatures (12°C). Pollen presentation is thus discontinued during periods where pollinators are not active. Overall stamen presentation increases with increasing flower age. Contrary to expectation, no geometrical correlation between the floral scale stimulated and the stamen fascicle reacting exists, indicating that the stimulus is transmitted over the receptacle and stamen maturation dictates which and how many stamens react. Thigmonastic stamen presentation is dramatically accelerated compared to autonomous movement (3–37 times), indicating that the rate of stamen maturation can be adjusted to different visitation schedules. Flowers can react relatively uniformly down to stimulation intervals of 10–15 min., consistently presenting comparable numbers of stamens in the flower c. 5 min. after the stimulus and can thus keep the amount of pollen presented relatively constant even under very high visitation frequencies of 4–6 visits/h. Thigmonastic pollen presentation dramatically reduces the overall duration of the staminate phase (to 1/3rd in Nasa macrothyrsa). Similarly, the carpellate phase is dramatically reduced after pollination, down to 1 d from 4 d. Overall flower longevity is reduced by more than 2/3rds under high visitation rates (<3 d versus 10 d under visitor exclusion) and depleted and pollinated flowers are rapidly removed from the pool. Complex floral behaviour in Loasaceae thus permits a near-total control over pollen dispensation schedules and floral longevity of the individual flower by an extraordinary fine-tuning to both biotic and abiotic factors.
Notes on the genus Caiophora (Loasoideae, Loasaceae) in Chile and neighbouring countries
Ackermann,Markus; Weigend,Maximilian;
Darwiniana , 2007,
Abstract: this is the first revision for the representatives of the genus caiophora (loasaceae) in chile. the genus is widely distributed in the andes from argentina/chile in the south to central ecuador in the north, and comprises approximately 60 species. in chile only five species are present, caiophora chuquitensis, c. cirsiifolia, c. coronata, c. deserticola sp. nov. and c. rosulata. caiophora rosulata is here subdivided into two subspecies: western andean c. rosulata subsp. rosulata (present in northern chile and southern peru), and eastern andean c. rosulata subsp. taraxacoides, stat. and comb. nov. furthermore c. superba syn. nov. and c. macrocarpa syn. nov. are placed into synonymy under c. chuquitensis, and c. rahmeri syn. nov. is synonymized to c. rosulata subsp. rosulata. these five species comprise the complete range of growth forms known for the genus, i.e., subshrubs, cushionforming herbs, acaulescent, rosulate herbs and vines. for all taxa a key and full morphological descriptions and synonymy are provided, including illustrations, notes on habitat, distribution, floral biology and chromosome numbers.
Notes on the genus Caiophora (Loasoideae, Loasaceae) in Chile and neighbouring countries
Markus Ackermann,Maximilian Weigend
Darwiniana , 2007,
Abstract: alrededor de 60 especies, y está ampliamente distribuido en los Andes, desde Argentina/Chile en el Sur, hasta el centro de Ecuador en el Norte. Se conocen solamente cinco especies de Chile: Caiophora chuquitensis, C. cirsiifolia, C. coronata, C. deserticola sp. nov. y C. rosulata. El material de Caiophora rosulata se divide entre dos subespecies, C. rosulata subsp. rosulata comb. nov., de los Andes Occidentales (presente en el norte de Chile y el sur de Perú, y C. rosulata subsp. taraxacoides stat. y comb. nov., de los Andes Orientales. Los nombres C. superba syn. nov. y C. macrocarpa syn. nov. son sinonimizados bajo C. chuquitensis, y C. rahmeri syn. nov., sinonimizado bajo C. rosulata subsp. rosulata. Estas cinco especies comprenden el rango completo de hábitos conocido para el género: sufrútices, hierbas perennes en forma de cojines, hierbas rosuladas acaules, y hierbas trepadoras. Proporcionamos una clave, descripciones morfológicas y la sinonimia completa para todos los taxones, incluyendo ilustraciones, notas sobre la distribución, el hábitat, la biología floral y números cromosómicos.
Phylogenetic insights into Andean plant diversification
Federico Luebert,Maximilian Weigend
Frontiers in Ecology and Evolution , 2014, DOI: 10.3389/fevo.2014.00027
Abstract: Andean orogeny is considered as one of the most important events for the development of current plant diversity in South America. We compare available phylogenetic studies and divergence time estimates for plant lineages that may have diversified in response to Andean orogeny. The influence of the Andes on plant diversification is separated into four major groups: The Andes as source of new high-elevation habitats, as a vicariant barrier, as a North-South corridor, and as generator of new environmental conditions outside the Andes. Biogeographical relationships between the Andes and other regions are also considered. Divergence time estimates indicate that high-elevation lineages originated and diversified during or after the major phases of Andean uplift (Mid-Miocene to Pliocene), although there are some exceptions. As expected, Andean mid-elevation lineages tend to be older than high-elevation groups. Most clades with disjunct distribution on both sides of the Andes diverged during Andean uplift. Inner-Andean clades also tend to have divergence time during or after Andean uplift. This is interpreted as evidence of vicariance. Dispersal along the Andes has been shown to occur in either direction, mostly dated after the Andean uplift. Divergence time estimates of plant groups outside the Andes encompass a wider range of ages, indicating that the Andes may not be necessarily the cause of these diversifications. The Andes are biogeographically related to all neighboring areas, especially Central America, with floristic interchanges in both directions since Early Miocene times. Direct biogeographical relationships between the Andes and other disjunct regions have also been shown in phylogenetic studies, especially with the eastern Brazilian highlands and North America. The history of the Andean flora is complex and plant diversification has been driven by a variety of processes, including environmental change, adaptation, and biotic interactions.
A new shrubby species of Nasa Weigend ser. Carunculatae (Urb. & Gilg) Weigend (Loasaceae) from the Amotape-Huancabamba Zone Nueva especie arbustiva de Nasa Weigend ser. Carunculatae (Urb. & Gilg) Weigend (Loasaceae) de la Zona Amotape-Huancabamba
Tilo Henning,Asunción Cano,Maximilian Weigend
Revista Peruana de Biología , 2011,
Abstract: Nasa is the largest genera in the Loasaceae family and it is particularly speciose in the Amotape-Huancabamba Zone of northern Peru. Nasa ser. Carunculatae is a group of four species, three of them endemic to the Amotape- Huancabamba Zone. Species in this group are characterized by their shrubby habit, deciduous leaves, and typical tilt-revolving flowers with white to greenish petals. In this work, we describe a new species of Nasa ser. Carunculatae from the southern limit of Amotape-Huancabamba area, La Libertad, Peru. The species differs from others in having much smaller and notably narrower leaves. Unlike all the other species of ser. Carunculatae, the entire distal portion of the stem is densely glandular. It is apparently most closely related to Nasa carunculata, a species known from inter-Andean valleys of Ancash and Ayacucho. Nasa es uno de los géneros más numerosos de la familia Loasaceae y en particular uno de los más especiosos en la zona de Amotape-Huancabamba. Nasa ser. Carunculatae es un grupo con cuatro especies, tres de las cuales son endémicas de la zona de Amotape-Huancabamba. Las especies de este grupo están caracterizadas por su hábito arbustivo, hojas deciduas y flores con pétalos blancos a verdosos del tipo con escamas florales que encierran al néctar y que obligan al polinizador a inclinarlas (“tilt-revolver flowers”). En el presente trabajo, nosotros describimos una nueva especie del grupo Nasa ser. Carunculatae, procedente del límite sur de la zona de Amotape-Huancabamba, La Libertad, Perú. La especie difiere por presentar hojas mucho más peque as y notablemente más angostas. A diferencia de las otras especies de la ser. Carunculatae, la porción distal del tallo es densamente glandular. Aparentemente está estrechamente relacionada a Nasa carunculata, una especie conocida de los valles interandinos de Ancash y Ayacucho.
Diversity patterns of selected Andean plant groups correspond to topography and habitat dynamics, not orogeny
Jens Mutke,Rana Jacobs,Tilo Henning,Maximilian Weigend
Frontiers in Genetics , 2014, DOI: 10.3389/fgene.2014.00180
Abstract: The tropical Andes are a hotspot of biodiversity, but detailed altitudinal and latitudinal distribution patterns of species are poorly understood. We compare the distribution and diversity patterns of four Andean plant groups on the basis of georeferenced specimen data: the genus Nasa (Loasaceae), the two South American sections of Ribes (sect. Parilla and sect. Andina, Grossulariaceae), and the American clade of Urtica (Urticaceae). There is a clear diversity peak between 3–8° S (Amotape-Huancabamba Zone, AHZ), with most narrowly endemic species found there across the groups studied. Latitudinal ranges are generally larger towards the margins of overall range of the group. In the tropical Andes species number and number of endemic species peak at elevations of 2,500–3,500 m, with high elevation species not notably different in latitudinal range. The ecological niches of the tropical groups studied are relatively similar in temperature and temperature seasonality, but do differ in moisture seasonality. This is mirrored in a particular diversity of growth form (as proxy for ecological niche) in the AHZ. Small scale climatic differences apparently contribute to spatial habitat heterogeneity, leading to increased diversity. Altitudinal diversity patterns correspond well with the altitudinal distribution of slope inclination, indicating that the likelihood and frequency of landslides translates into temporal habitat heterogeneity: since most of the taxa studied are from disturbed and secondary vegetation, the frequency of landslides may be causally connected to diversification. Overall, spatiotemporal habitat heterogeneity appears to be directly and positively correlated to diversity and endemicity. Conversely, uplift history is not reflected in the pattern here retrieved, since the AHZ is the area of the most recent Andean uplift. Similarly, a barrier effect of the low-lying Huancabamba depression is not at all visible in our data.
The conductance of molecular wires and DFT based transport calculations
F. Evers,F. Weigend,M. Koentopp
Physics , 2003,
Abstract: The experimental value for the zero bias conductance of organic molecules coupled by thiol-groups to gold electrodes tends to be much smaller than the theoretical result based on density functional theory (DFT) calculations, often by orders of magnitude. To address this puzzle we have analyzed the regime within which the approximations made in these calculations are valid. Our results suggest that a standard step in DFT based transport calculations, namely approximating the exchange-correlation potential in quasistatic nonequilibrium by its standard equilibrium expression, is not justified at weak coupling. We propose, that the breakdown of this approximation is the most important source for overestimating the width of the experimentally observed conductance peak and therefore also of the zero bias conductance. We present a numerical study on the conductance of the organic molecule that has recently been studied experimentally by Reichert et. al. (PRL 88, 176804 (2002)) that fully agrees with this conclusion.
Population Genomic Analyses Based on 1 Million SNPs in Commercial Egg Layers
Mahmood Gholami, Malena Erbe, Christian G?rke, Rudolf Preisinger, Annett Weigend, Steffen Weigend, Henner Simianer
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0094509
Abstract: Identifying signatures of selection can provide valuable insight about the genes or genomic regions that are or have been under selective pressure, which can lead to a better understanding of genotype-phenotype relationships. A common strategy for selection signature detection is to compare samples from several populations and search for genomic regions with outstanding genetic differentiation. Wright's fixation index, FST, is a useful index for evaluation of genetic differentiation between populations. The aim of this study was to detect selective signatures between different chicken groups based on SNP-wise FST calculation. A total of 96 individuals of three commercial layer breeds and 14 non-commercial fancy breeds were genotyped with three different 600K SNP-chips. After filtering a total of 1 million SNPs were available for FST calculation. Averages of FST values were calculated for overlapping windows. Comparisons of these were then conducted between commercial egg layers and non-commercial fancy breeds, as well as between white egg layers and brown egg layers. Comparing non-commercial and commercial breeds resulted in the detection of 630 selective signatures, while 656 selective signatures were detected in the comparison between the commercial egg-layer breeds. Annotation of selection signature regions revealed various genes corresponding to productions traits, for which layer breeds were selected. Among them were NCOA1, SREBF2 and RALGAPA1 associated with reproductive traits, broodiness and egg production. Furthermore, several of the detected genes were associated with growth and carcass traits, including POMC, PRKAB2, SPP1, IGF2, CAPN1, TGFb2 and IGFBP2. Our approach demonstrates that including different populations with a specific breeding history can provide a unique opportunity for a better understanding of farm animal selection.
Bottom Mass from Nonrelativistic Sum Rules at NNLL
Stahlhofen, Maximilian
High Energy Physics - Phenomenology , 2013,
Abstract: We report on a recent determination of the bottom quark mass from nonrelativistic (large-n) Upsilon sum rules with renormalization group improvement (RGI) at next-to-next-to-leading logarithmic (NNLL) order. The comparison to previous fixed-order analyses shows that the RGI computed in the vNRQCD framework leads to a substantial stabilization of the theoretical sum rule moments with respect to scale variations. A single moment fit (n=10) to the available experimental data yields M_b^{1S}=4.755 +- 0.057(pert) +- 0.009(alpha_s) +- 0.003(exp) GeV for the bottom 1S mass and m_b(m_b)= 4.235 +- 0.055(pert) +- 0.003(exp) GeV for the bottom MSbar mass. The quoted uncertainties refer to the perturbative error and the uncertainties associated with the strong coupling and the experimental input.
Vom Rosenkranz zum Mambo. Zu den vermeintlich afrikanischen Wurzeln afroamerikanischer Musik
Hendler, Maximilian
Samples : Notizen, Projekte und Kurzbeitr?ge zur Popularmusikforschung , 2001,
Abstract:
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